Pre-Shot Simulations of Far-Field Ground Motions for the Source Physics Experiment (SPE) Explosions at the Climax Stock, Nevada National Security Site

Abstract

The Source Physics Experiment (SPE) will involve a series of explosions in various geologic and emplacement conditions to validate numerical simulation methods to predict behavior of seismic wave excitation and propagation for nuclear test monitoring. The first SPE's currently underway involve explosions in the Climax Stock (granitic geology) at the Nevada National Security Site (NNSS). Detailed geologic data and published material properties for the major lithologic units of the NNSS and surrounding region were used to build three-dimensional models for seismic wave propagation simulations.The geologic structure near the SPE shot point is quite varied including granitic, carbonate, tuff and alluvium lithologies. We performed preliminary ground motion simulations for a near-source domain covering 8 km x 8 km at the surface centered on the shot point to investigate various source and propagation effects using WPP, LLNL's anelastic seismic wave finite difference code. Simulations indicate that variations in wave propagation properties of the sub-surface will generate strongly path-dependent response once the energy has left the relatively small granitic geology of the near-surface Climax Stock near the SPE shot point. Rough topography to the north and west of SPE shot point causes additional complexity in the signals including energy on the transverse components. Waves propagate much faster through the granitic and carbonate formations and slower through the tuff and alluvium. Synthetic seismograms for a pure explosion

Pre-Shot Simulations of Near-Field and Far-Field Ground Motion for the Source Physics Experiment (Spe) Explosions at the Climax Stock, Nevada National Security Site: Spe3

“…Semi-empirical approaches do not have frequency limits but include a priori assumptions. Prior to the SPE1 shot, a comprehensive numerical modeling effort was undertaken and presented in Rodgers et al [2010]. The modeling used an advanced finite-difference algorithm (WPP) [Petersson and Sjogreen, 2009Sjogreen and Petersson, 2010] to conduct 3D modeling of the seismic waveforms at distance up to 4 km from the source.…”

“…Prior to the SPE1 shot, a comprehensive numerical modeling effort was undertaken and presented in Rodgers et al [2010]. The modeling used an advanced finite-difference algorithm (WPP) [Petersson and Sjogreen, 2009Sjogreen and Petersson, 2010] to conduct 3D modeling of the seismic waveforms at distance up to 4 km from the source. WPP has the capability to handle 3D variations in the material properties (density, compressional and shear wavespeed and the attenuation factor, Q) and a variety of sources including point sources and extended sources using the moment tensor representation.…”

“…This report is intended to serve as a summary of the pre-shot simulation of the 'far-field' effects of the July 24, 2012 shot (SPE3). By 'far-field' we refer to distances at which seismic wave propagation is primarily elastic [Rodgers et al, 2010].…”